IllegalArgumentException e =
        assertThrows(
            IllegalArgumentException.class, () -> networkAsMutableNetwork.addEdge(N1, N1, E11));
    assertThat(e).hasMessageThat().contains(ERROR_SELF_LOOP);
  }

  /**
   * This test checks an implementation dependent feature. It tests that the method {@code addEdge}
   * will silently add the missing nodes to the graph, then add the edge connecting them. We are not

    IllegalArgumentException e =
        assertThrows(
            IllegalArgumentException.class, () -> networkAsMutableNetwork.addEdge(N1, N1, E11));
    assertThat(e).hasMessageThat().contains(ERROR_SELF_LOOP);
  }

  /**
   * This test checks an implementation dependent feature. It tests that the method {@code addEdge}
   * will silently add the missing nodes to the graph, then add the edge connecting them. We are not